When using low noise amplifiers (LNAs), such as LNAs used in charge to digital conversion systems for x-ray and CT scan equipment, care must be taken to minimize circuit noise. In particular, it is desirable to provide very low noise amplification of sensor signals to minimize a dosage amount needed to perform x-ray and CT scan imaging. As amplitude of an input signal to an amplifier is decreased, an amount of circuit noise that can be tolerated also decreases. Source, biasing, and feedback resistors associated with an LNA each contribute to circuit noise, such as in the form of Johnson noise and/or noise generated by input currents into the amplifier. Typically, noise at the output of the amplifier may is characterized as the root mean square sum of the noise from the sensor, the amplifier, and the biasing circuit.
In the past, low noise biasing of LNAs used in x-ray and CT applications has been achieved using relatively large, high power consuming transistors and/or relatively expensive devices, such as BiCMOS devices. To economize on space and power requirements, an LNA biasing circuit may be shared among multiple channels of an amplification stage to reduce circuit area and power consumption requirements. However, such configurations may lead to crosstalk and correlated noise across the multiple channels. Accordingly, improved low noise biasing of LNAs is desired.